Evaluation of LBBB Patients
October 1, 1998 3 minutes read
Evaluation of LBBB Patients
ABSTRACT & COMMENTARY
Synopsis: In patients with LBBB and normal LV function suspected of having IHD, a negative dipyridamole thallium scan confirmed an excellent prognosis.
Source: Gil VM, et al. J Nucl Cardiol 1998;5:414-417.
Left bundle branch block (lbbb) in an adult usually means cardiomyopathy or coronary artery disease. If echocardiography shows normal left ventricular function, what should be the next test? Gil and associates assessed the hypothesis that dipyridamole thallium perfusion scintigraphy could accurately assess prognosis in such patients. Thus, they retrospectively evaluated 142 patients with LBBB referred for dipyridamole thallium because of suspected ischemic heart disease (IHD) and selected 69 with normal scans. All the patients had normal LV function by echocardiography, and their pre-test likelihood of IHD was low to intermediate based upon clinical and risk factor assessment. Of these 69, 63 had chest pain, and six were asymptomatic, and only 12 had no risk factors for IHD. The 36 women and 33 men aged 56-61 years were followed for an average of 33 months (range 25-35). During follow-up, four developed unstable angina-two of whom underwent myocardial revascularization. There were no deaths or myocardial infarctions, and all the events occurred two or more years after study enrollment. Among 48 patients with equivocal scans, one died during follow-up, and six underwent coronary angiography, all normal. Among 25 patients with definite perfusion defects, there were no deaths, but 15 underwent catheterization that showed significant coronary lesions in nine-eight of whom had revascularization. Gil et al conclude that in patients with LBBB and normal LV function suspected of having IHD, a negative dipyridamole thallium scan confirmed an excellent prognosis. They suggested that such patients do not need coronary angiography to clarify the etiology of the LBBB.
COMMENT BY MICHAEL H. CRAWFORD, MD
Epidemiologic studies have shown that LBBB is more common in men who were advancing in age. The most frequent diseases associated with LBBB are hypertension, dilated cardiomyopathy, and IHD, respectively. Thus, LBBB should be evaluated further, and this study assesses the appropriate diagnostic approach.
After the history and physical examination, an echocardiogram is the usual first step. Echo will identify those with LV hypertrophy, dilated cardiomyopathy, and remote myocardial infarction. Further evaluation of those with a normal echo involves physician judgment. If IHD is suspected because of the history and risk profile dipyridamole perfusion scintigraphy seems to be a good test based upon this study. Other studies have suggested that dipyridamole avoids the false-positive scan problem of exercise testing in patients with LBBB. Some believe adenosine is even better because it is less likely to induce myocardial ischemia. How well dobutamine echo would perform in this situation is not known, but some studies have suggested an increased incidence of false-positive abnormal septal motion in patients with LBBB given dobutamine.
The major limitation of this study is that it assessed a low-risk population with normal echoes and a low pretest likelihood of IHD. Thus, the lack of events may reflect the population as much as the negative scan. It would have been interesting to assess prognosis based upon the clinical evaluation alone and determine the additive value of dipyridamole thallium. When such an analysis has been done in other settings (i.e., preoperative risk assessment), the clinical evaluation has faired well. Regardless, it does not appear that coronary angiography is necessary to evaluate all patients with LBBB.
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